Non-alcoholic fatty liver disease (NAFLD) is a spectrum of conditions marked by fatty infiltration of the liver (steatosis) and sometimes histologic evidence of inflammation (steatohepatitis) without a history of excessive alcohol ingestion. NAFLD is common and is strongly associated with obesity, insulin resistance (IR), and T2DM, three conditions with strong evidence for genetic pathogenesis; however, the genetic epidemiology of NAFLD is not well characterized. The central hypothesis of the proposed research is that NAFLD, for any given degree of adiposity, is highly familial and that genetic variations can explain not only difference in risk and severity of hepatic steatosis but also risk of T2DM between individuals. To test this hypothesis, we propose the following specific aims: (1) characterize the distribution of NAFLD using non-contrast electron beam computed tomography in a cohort of 1,000 participants of the Amish Family Calcification Study [AFCS]; 2) estimate the relative contributions of genes and measured environmental risk factors markers of NAFLD; 3) evaluate familial clustering among obesity, IR, NAFLD, T2DM and to determine the extent to which common genetic factors influence variation in these traits jointly (i.e. pleiotropy), (4) perform a genome-wide linkage analyses of markers of NAFLD and T2DM in the AFCS, (5) perform genetic association analyses of markers of NAFLD and T2DM and single nucleotide polymorphisms from candidate genes in chromosome regions identified by linkage analysis in AFCS and a subgroup of individuals from the Action for Health in Diabetes (Look AHEAD) Study. The proposed research builds on Dr. Kao's focus on the genetic epidemiology of obesity and T2DM. She will be assisted by mentors with expertise in medicine, epidemiology, statistics and molecular genetics. The new methods and expertise acquired as a result of this Career Development Award will equip Dr. Kao with the tools necessary to launch a fully independent career in genetic epidemiological research. This proposal is strengthened by: focus on a novel diabetes-related endophenotype; large sample of highly-informative families for linkage analyses (AFCS); availability of confirmed unrelated NAFLD cases for association analyses (Look AHEAD), assessment of a multitude of cardiovascular and environmental risk factors; state-of-the-art imaging of the liver; and comprehensive genetic analyses, including both genome-wide and candidate gene approaches. A deeper understanding of the molecular pathogenesis of obesity, IR, NAFLD, and T2DM may suggest new approaches for the prevention and treatment of these conditions.